This invention relates to a method of and apparatus for removing metallic impurities diffused in a semiconductor substrate, and more particularly to a method of and apparatus capable of effectively removing metallic impurities diffused in a substrate, which could not be removed by conventional wet cleaning methods.
Wet cleaning techniques have been widely used to remove metallic impurities on the surface of a silicon substrate. A typical one of the wet cleaning techniques is the RCA method. This method is strictly intended for cleaning the surface of a silicon substrate, so it cannot be applied to the removal of metallic impurities diffused in a silicon substrate.
Therefore, to remove metallic impurities from silicon substrates, gettering techniques classified as intrinsic gettering (IG) and extrinsic gettering (EG) have been used. The gettering techniques are the techniques for trapping metallic impurities diffused in a silicon substrate in a place away from an active-layer-forming area, that is, in a gettering site.
Intrinsic gettering (IG) is a gettering technique where a gettering site is formed in the substrate. Extrinsic gettering (EG) is a gettering technique where a gettering site is formed at the front or back surface of the substrate.
Intrinsic gettering is the gettering technique making use of an oxygen precipitation phenomenon taking place in a CZochralski(CZ) silicon crystal. Specifically, with the technique, a defect-free region is formed at the surface layer of a silicon substrate and at the same time, a bulk defect is forced to develop in the silicon substrate. Then, metallic impurities diffused in the silicon substrate are caused to precipitate in the distorted field (IG layer) around the defect, thereby suppressing the precipitation of metallic impurities in the active layer in the defect-free region.
By the gettering technique, however, metallic impurities are just trapped from the active layer into the gettering site and not removed from the substrate. This causes the problem that the metallic impurities trapped in the gettering site are released from the gettering site and contaminate the active layer in subsequent high-temperature processes.